Zero current switching

ABSTRACT

A method for providing non-resonant zero-current switching in a switching power converter operating in a continuous current mode. The switching power converter converts power from input power to output power. The switching power converter includes a main switch connected to a main inductor, wherein an auxiliary inductor is connectible with the main inductor. The main current flows from an input to an output. The auxiliary inductor is connected with the main inductor thereby charging the auxiliary inductor so that an auxiliary current flows from the output to the input opposing the main current. Upon a total current including a sum of the main current and the auxiliary current. substantially equals or approaches zero, the switch is turned on.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application benefits from U.S. provisional application61/039,046 filed on Mar. 24, 2008 by the present inventors.

BACKGROUND

1. Technical Field

The present invention relates to switching converters and tospecifically a method and devices for zero current switching forreducing switching losses in switching converters.

2. Description of Related Art

FIG. 1 shows a typical conventional buck-boost DC-to-DC convertercircuit 10. The buck circuit of buck-boost DC-to-DC converter 10 has aninput voltage V_(in) with an input capacitor C₁ connected in parallelacross V_(in). Two switches are implemented as field effect transistors(FET) with integral diodes: a high side buck switch Q₁ and a low sidebuck switch Q₂ connected in series by connecting the source of Q₁ to thedrain of Q₂. The drain of Q₁ and the source of Q₂ are connected parallelacross an input capacitor C₁. A node A is formed between switches Q₁ andQ₂ to which one end of an inductor 106 is connected. The other end ofinductor 106 is connected to the boost circuit of buck-boost DC-to-DCconverter 10 at a node B. Node B connects two switches: a high sideboost switch Q₄ and a low side boost switch Q₃ together in series wherethe source of Q₄ connects to the drain of Q₃ to form node B. The drainof Q₄ and the source of Q₃ connect across an output capacitor C₂ toproduce the output voltage V_(out) of buck-boost DC-to-DC converter 10.

FIG. 2 a illustrates the buck phase or on-state circuit of DC-to-DCconverter circuit 10 shown in FIG. 1, the input voltage source V_(in) isdirectly connected to inductor 106 and the load is isolated from V_(in)because Q₁ is on, Q₂ is off, Q₃ is on and Q₄ is off. These switchpositions: Q₁ on, Q₂ off, Q₃ on and Q₄ off; result in accumulatingenergy in inductor 106 since source V_(in) is directly connected toinductor 106. In the on-state, output capacitor C₂ supplies energy tothe load.

FIG. 2 b illustrates the boost phase or off-state circuit of DC-to-DCconverter circuit 10, Inductor 106 is connected in parallel across theload and capacitor C₂ because Q₁ is off, Q₂ is on, Q₃ is off and Q₄ ison. Q₁ being off isolates inductor 106 from the input voltage (V_(in))and capacitor (C₁). The stored energy in inductor 106 (as a result ofthe previous On-state) is transferred from inductor 106 to C₂ and theload.

Two common methods of operating DC-to-DC converter circuit 10 are ineither continuous mode or discontinuous mode. If the current through theinductor 106 never falls to zero during a commutation cycle (i.e. thetime period to perform both the on-state and the off-state), DC-to-DCconverter circuit 10 is said to operate in continuous mode and typicallythe on-state operates for a shorter period of time when compared to theoff-state. Discontinuous mode of operation for DC to DC convertercircuit 10 occurs when the amount of energy required by the load issmall enough to be transferred in a time period smaller than the wholecommutation cycle. Typically, the current through inductor 106 falls tozero for a short time period after the off-state period and thereforeinductor 106 is completely discharged at the end of the commutationcycle. The commutation cycle therefore includes the on-state, theoff-state and the short time period during which the inductor current iszero.

A conventional “resonant” method for achieving virtually zero power losswhen switching a switch is to apply a direct current voltage inputvoltage V_(in) across a switch (with a diode connected across theswitch, the diode is reverse biased with respect to V_(in)) in serieswith an inductor L and a capacitor C. The output voltage of the circuitis derived across the capacitor. The output voltage of the circuit couldthen in principle be connected to the input of a power converter, forexample a buck-loaded series tank circuit with load. The resonantfrequency of the series inductor L and capacitor C is given by Eq. 1 andthe corresponding resonant periodic time T given in Eq. 2.f ₀=½π(LC)^(1/2)  Eq.1T=1/f ₀  Eq.2

A pulse response of the circuit means that when the switch turns on,there is both zero current in the inductor and zero voltage across thecapacitor (Power=Volts×Current=0×0=zero power loss at turn on). Duringsteady state operation of the circuit, the inductor current andcapacitor voltage are sinusoidal and have a 90 degrees phase shift withrespect to each other. When the switch turns off (the on period of theswitch corresponds to half of the resonant periodic time) there is zerocurrent in the inductor and maximum positive voltage (i.e.V_(capacitor)=V_(in)) across the capacitor(Power=Volts×Current=V_(in)×0=zero power loss at turn off).

BRIEF SUMMARY

According to the present invention there is provided a method forproviding non-resonant zero-current switching in a switching powerconverter operating in a continuous current mode. The switching powerconverter converts power from input power to output power. The switchingpower converter includes a main switch connected to a main inductor,wherein an auxiliary inductor is connected in parallel with the maininductor. The main current flows from an input to an output. Theauxiliary inductor is connected with the main inductor thereby chargingthe auxiliary inductor so that an auxiliary current flows from theoutput to the input opposing main current. Upon a total currentincluding a sum of the main current and the auxiliary current.substantially equals or approaches zero, the main switch is turned on.When the auxiliary current is or approaches zero current the auxiliaryinductor is disconnected from the main inductor.

According to the present invention there is provided a switchingconverter including a buck stage or a boost stage or a buck-boost stageincluding: a main switch connecting an input voltage terminal to a firstnode, a main inductor connected at one end to the first node and at theother end operatively connected at a second node to a voltage output;and an auxiliary inductor adapted for connecting in parallel with themain inductor between the first and second nodes. Upon connecting theauxiliary inductor with the main inductor, the auxiliary inductor ischarged so that an auxiliary current flows from the second node to thefirst node opposing the main current flowing between the first andsecond nodes through the main inductor. The total current includes a sumof the main current and the auxiliary current. When the total currentsubstantially equals or approaches zero. The main switch is switched on.Energy stored within the auxiliary inductor is substantially allavailable for converting to output power by the switching converter. Thecurrent of the auxiliary inductor is naturally discharged to the inputand/or the output. When the auxiliary current approaches zero, theauxiliary inductor is disconnected from the main inductor. The switchingconverter may include a first auxiliary switch adapted for connectingthe auxiliary inductor to the first node; a second auxiliary switchadapted for connecting the auxiliary inductor to the second node. Adischarge diode for discharging the auxiliary inductor is connectedbetween the auxiliary conductor and a second input voltage terminal orground in case of reverse current in the auxiliary inductor due toreverse recovery charge of one of the auxiliary switches. The first andsecond auxiliary switches are typically implemented as field-effecttransistors each with parasitic diodes, with the parasitic diodesconnected in opposite directions. The main switch is usually any of a:silicon controlled rectifier (SCR), insulated gate bipolar junctiontransistor (IGBT), bipolar junction transistor (BJT), field effecttransistor (FET), junction field effect transistor (JFET), switchingdiode, electrical relay, reed relay, solid state relay, insulated gatefield effect transistor (IGFET), diode for alternating current (DIAC),and/or triode for alternating current TRIAC.

According to the present invention there is provided a plurality of mainswitches interconnected in a bidirectional current full bridge topology,the main switches including a first switch, a second switch, a thirdswitch and a fourth switch. A pair of input voltage terminals areattachable at a first node connecting the first and third switches andat a second node connecting the second and fourth switches. A firstoutput voltage terminal is operatively attached at a third nodeconnecting the third and fourth switches and a second output voltageterminal is operatively attached at a fourth node connecting the firstand second switches. A first main inductor or a single inductor and someother circuitry (a transformer for example) first node is attachablebetween the first output voltage terminal and the third node and asecond main inductor or a single inductor and some other circuitrysecond node attachable between the second output voltage terminal andthe fourth node. An auxiliary inductor is connectible between the thirdnode and the fourth node. Upon connecting the auxiliary inductor withthe first and/or second main inductors or single inductor withcircuitry, the auxiliary inductor is charged so that an auxiliarycurrent flows between the third node and the fourth node. The auxiliarycurrent opposes the main current. The total current includes a sum ofthe main current and the auxiliary current.

When the total current substantially equals or approaches zero, the mainswitches are switched (on). The current of the auxiliary inductor isnaturally discharged to the input and/or the output. When the auxiliarycurrent approaches zero, the auxiliary inductor is disconnected from themain circuit. Energy stored within the auxiliary inductor issubstantially all available for converting to output power by theswitching converter. A first auxiliary switch is preferably adapted forconnecting the auxiliary inductor to the third node and a secondauxiliary switch is adapted for connecting the auxiliary inductor to thefourth node. One or two discharge diodes are preferably connectedbetween said auxiliary conductor to the second node. The dischargediodes serve to protect against reverse recovery current of theauxiliary switches, depending on the main current direction. The firstand second auxiliary switches are typically implemented as field-effecttransistors each with parasitic diodes; the parasitic diodes areconnected on opposite directions. The first inductor and the secondinductor are preferably split inductors. The main switches are siliconcontrolled rectifier (SCR), insulated gate bipolar junction transistor(IGBT), bipolar junction transistor (BJT), field effect transistor(FET), junction field effect transistor (JFET), switching diode,electrical relay, reed relay, solid state relay, insulated gate fieldeffect transistor (IGFET), diode for alternating current (DIAC), and/ortriode for alternating current TRIAC.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 shows a typical conventional buck-boost DC-to-DC convertercircuit;

FIG. 2 a illustrates the buck phase or on-state circuit of conventionalDC-to-DC converter circuit;

FIG. 2 b illustrates the boost phase or off-state circuit of DC-to-DCconverter circuit;

FIG. 3 illustrates a buck-boost DC-to-DC converter, according to anembodiment of the present invention;

FIGS. 3 a-3 e illustrate operation of the buck-boost DC-to-DC converter,according to the embodiment of FIG. 3;

FIG. 4 shows a flow diagram of a method for zero current switching,running in continuous mode during the turn on of a main switch accordingto embodiments of the present invention;

FIG. 5 shows another embodiment of present invention as applied to afull bridge switched DC-to-DC converter;

FIGS. 5 a-5 e illustration operation according to the embodiment of FIG.5; and

FIG. 6 shows a timing diagram of selected voltages and currents in theembodiment of the present invention according to FIG. 5.

The foregoing and/or other aspects will become apparent from thefollowing detailed description when considered in conjunction with theaccompanying drawing figures.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

DEFINITIONS

The term switch as used herein refers to any of: silicon controlledrectifier (SCR), insulated gate bipolar junction transistor (IGBT),bipolar junction transistor (BJT), field effect transistor (FET),junction field effect transistor (JFET), switching diode, mechanicallyoperated single pole double pole switch (SPDT), SPDT electrical relay,SPDT reed relay, SPDT solid state relay, insulated gate field effecttransistor (IGFET), diode for alternating current (DIAC), and triode foralternating current (TRIAC).

The term “zero current switching” (or “ZCS”) as used herein is when thecurrent through a switch is reduced to significantly zero amperes priorto when the switch is being turned either on or off.

The term “power converter” as used herein applies to DC-to-DCconverters, AC-to-DC converters, DC-to-AC inverters, buck converters,boost converters, buck-boost converters, full-bridge converters andhalf-bridge converters or any other type of electrical powerconversion/inversion known in the art.

The term “zero voltage switching” (or “ZVS”) as used herein is that thepeak voltage across a switch, is reduced to substantially zero voltswhen the switch is being turned either on or off.

The term “cycle” or “commutation cycle” refers to the periodicity ofmain switch positions in a circuit which performs a process ofelectrical power conversion or inversion.

The term “non-resonant” as used herein to exclude resonant andquasi-resonant circuits used in the prior art for zero currentswitching. Resonant switching implies that the switching frequencies aresimilar to a resonant frequency of a resonant tank circuit in theswitching converter.

The terms “charging” and “discharging” in the context of the presentinvention in reference to charging and discharging a capacitor, are usedherein interchangeably except that current flow while charging anddischarging is usually in the opposite direction.

Reference is now made to FIG. 3 (including FIGS. 3 a-3 e) showing abuck-boost DC-to-DC converter 30 according to an embodiment of thepresent invention. A buck circuit 32 of buck-boost DC-to-DC converter 30has an input voltage V_(in) with an input capacitor C₁ connected inparallel across V_(in). Two switches Q₁ and Q₂ are connected in seriesat node A by connecting the source of Q₁ to the drain of Q₂. The drainof Q₁ and the source of Q₂ are placed in parallel across capacitor C₁.The source of Q₂ is connected to ground. The other end of inductor 106is connected in the present example to a boost circuit 34 of buck boostDC-to-DC converter 30 at node B.

A zero-voltage switching feature according to embodiments of the presentinvention is provided using switch module 300. Switch module 300 has aswitch Q₅, the drain of Q₅ is connected to node A of buck circuit 32 vialink 308. The source of Q₅ connects to one end of an auxiliary inductor302 to form a node E. A cathode of discharge diode D₁ connects to node Eand the anode of discharge D₁ connects to ground. The other end ofauxiliary inductor 302 connects to the source of switch Q₆. The drain ofQ₆ connects to node B of boost circuit 34 via a link 310.

Reference is still made to buck-boost DC-to-DC converter 30 shown inFIGS. 3 a-3 e which illustrate operation of buck-boost DC-to-DCconverter 30 and FIG. 4 showing a flow diagram of a method for zerocurrent switching, for zero current switching in boost and/or bucktopologies running in continuous mode during the turn on of main switchQ₃ and/or Q₁ according to embodiments of the present invention.Throughout the following illustration using FIGS. 3 a-3 e, an electricalproperty of an inductor is relied upon; namely that when a voltage V isapplied across an inductor, the initial current through the inductor iszero and after a certain time period inductor current I_(L) builds uplinearly. In FIGS. 3 a-3 e, current flow in buck circuit 32, boostcircuit 34 and switch module 300 is indicated by arrow markings and grayshaded lines.

-   A. Reference is now made to FIG. 3 a which illustrates the state of    DC-to-DC converter 30 prior to buck turn on. Switch Q₂ is on.    Switches Q₁, Q₅ and Q₆ are off. Current flows through inductor 106    from node A to node B and switch Q₂. Switch Q₂ turns off and current    continues to flow through the parasitic diode of switch Q₂.-   B. Reference is now made to FIG. 3 b which continuous to illustrate    the state of DC-to-DC converter 30 prior to buck leg turn on.    Switches Q₅ and Q₆ turn on at zero current at I_(aux). Current    I_(aux) through auxiliary conductor and switches Q₅ and Q₆ increases    linearly as auxiliary inductor 302 is charged by output voltage    V_(out). The direction of current I_(aux) opposes current I_(p)    through main inductor 106 and flows from node B to node A. Switches    Q₁, and Q₂, are off but current I_(p) flows through inductor 106    from node A to node B through the parasitic diode of switch Q₂.-   C. Reference is now made to FIG. 3 c which illustrates the state of    DC-to-DC converter 30 as buck leg turns on. When current I_(aux)    equals current I_(p) through inductor 106 plus Q₂ diode recovery    current, the voltage V_(buck) across Q₂ starts to rise. Switch Q₁    then turns on at zero current. Switch Q₂ remains off. Switches Q₅    and Q₆ remain on and I_(aux) begins to decrease discharging from    V_(in) to V_(out).-   D. Reference is now made to FIG. 3 d which continues to illustrate    the state of DC-to-DC converter 30 as buck leg turns on; Q₅ turns    off when current through I_(aux) gets low (i.e. substantially zero    current switching), the current I_(aux) flows through Q₅ parasitic    diode. The current I_(aux) reverses because of Q₅ reverse recovery    current. This reverse recovery current discharges through the    discharge diode D₁ and Q₆.-   E. Reference is now made to FIG. 3 e which illustrates the state of    DC-to-DC converter 30 after buck leg turns on. Current I_(p) flows    through switch Q₁ through inductor 106 and through boost circuit 34.    Current I_(aux) falls to zero and switch Q₆ is turned off.

FIG. 4 shows a simplified flow diagram of a method for zero currentswitching according to an embodiment of the present invention. Stillreferring to the embodiment of FIG. 3, in step 41, auxiliary inductor302 is connected to main inductor 106 in parallel by auxiliary switchesQ₅ and Q₆. When the total current is substantially zero in decision box43, main switch Q₁ is switched on (step 45) at zero current. A preferredmethod of determining when the total current reached is zero is to use azero current sensing circuit or to turn Q₁ on at a time according to thetiming transients of either auxiliary inductor 302 or inductor 106. Whenthe current in auxiliary inductor 302 is substantially zero in decisionbox 47, auxiliary switch Q₆ is switched off (step 49) at zero currentand inductor 302 is disconnected across inductor 106. A preferred methodof determining when the current in auxiliary inductor 302 approacheszero current, is to use a zero current sensing circuit or to turn Q₆ offat a time according to the timing transients of either auxiliaryinductor 302 or inductor 106.

FIG. 5 shows a further embodiment of present invention as applied to afull bridge DC to DC converter 50. Full bridge DC to DC converter 50 hasfour main switches S_(m,1), S_(m,2), S_(m,3) and S_(m,4) connectedtogether in a full bridge configuration. Each of four main switches(S_(m,1), S_(m,2), S_(m,3) and S_(m,4)) have respective diode shuntsconnected in parallel thereto. The diodes placed across switches S_(m,1)and S_(m,2) are in both the same direction similarly the diodes ofS_(m,3) and S_(m,4) are both in the same direction. All diodes connectedacross switches S_(m,1), S_(m,2), S_(m,3) and S_(m,4) are reverse biasedwith respect to the input voltage V_(in). An input voltage (V_(in) ⁻) offull bridge DC-to-DC converter 50 is connected across the node betweenswitches S_(m,2) and S_(m,4) and an input voltage (V_(in) ⁺) isconnected at the node between switches S_(m,1) and S_(m,3). An outputvoltage (V_(out) ⁻) of full bridge DC-to-DC converter 50 is connectedacross the node (M) between switches S_(m,1) and S_(m,2) connectedthrough a split inductor 500 a and output voltage V_(out)+ is connectedat the node (L) between switches S_(m,3) and S_(m,4) through a splitinductor 500 b. An auxiliary switch S_(a,1) is connected between nodes Mand K. A diode is placed across in parallel with S_(a,1) with thecathode of the diode connected to node M and the anode of the diodeconnected to node K. A discharge diode D₁ is connected between node Kand V_(in) ⁻ with the anode of D₁ connected to V_(in) ⁻ and the cathodeof D₁ connected to node K. One end of an auxiliary inductor 502 connectsto node K. The other end of auxiliary inductor 502 connects to node J. Adischarge diode D₂ is connected between node J and V_(in) ⁻ with theanode of D₂ connected to V_(in) ⁻ and the cathode of D₂ connected tonode J. An auxiliary switch S_(a,2) is connected between nodes J and L.A diode is placed across in parallel with S_(a,2) with the cathode ofthe diode connected to node L and the anode of the diode connected tonode J.

The operation of full bridge circuit 50, according to a feature of thepresent invention is illustrated with reference also to FIGS. 5 a-5 eand FIG. 6 which shows a timing diagram of selected voltages andcurrents for steps V to Z is as follows:

FIGS. 5 a-5 e illustrate current flow is indicated by arrow markings andgray shaded lines.

-   V) Referring now specifically to FIG. 5 a: Main switches S_(m,1) and    S_(m,4) are turned on, all other switches are off. Current I_(p)    flows from V_(out) ⁻ to V_(in) ⁺ through inductor 500 a, and through    main switch S_(m,1). Current flows from V_(in) ⁻ to V_(out) ⁺    through main switch S_(m,4) and through inductor 500 b.-   W) Referring now specifically to FIG. 5 b; Switches S_(m,1) and    S_(m,4) are turned off. Switches S_(a,1) and S_(a,2) are turned on.    Current I_(aux) begins at zero current and increases linearly,    current I_(aux) flowing between nodes M and L. Because the current    I_(aux) is initially zero, the switching on of switches S_(a,1) and    S_(a,2), occurs with zero current. Current flows from V_(out) ⁻ to    V_(in) ⁺ through inductor 500 a, and through the diode of main    switch S_(m,1) Current flows from V_(in) ⁻ to V_(out) ⁺ through the    diode of main switch S_(m,4) and through inductor 500 b.-   X) Referring now specifically to FIG. 5 c; Once the auxiliary    current I_(aux) reaches a peak value, equaling to I_(p), main    switches S_(m,2) and S_(m,3) are turned on with zero current since    Kirchhoff's current equation at node M shows current through main    switch S_(m,2): IS_(m,2)=I_(P)−I_(aux)=0 and Kirchhoff's current    equation at node L shows IS_(m,3)=I_(P)−I_(aux)=0. Current flows    from V_(in) ⁺ to V_(out) ⁺ through main switch S_(m,3), and through    inductor 500 b. Current now flows from V_(out) ⁻ to V_(in) ⁻ through    inductor 500 a and through main switch S_(m,2.)-   Y) Referring now specifically to FIG. 5 d; Auxiliary switch S_(a,2)    is now turned off as current I_(aux) has reduced to substantially    zero in the direction of node M to node L. Diode D₂ takes any    reverse recovery current from switch S_(a,2). Current flows into    V_(out)+ from V_(in) ⁺ through inductor 500 b, and through main    switch S_(m,3) Current now flows into V_(in) ⁻ from V_(out) ⁻    through main switch S_(m,2) and through inductor 500 a.-   Z) Referring now specifically to FIG. 5 e; Auxiliary switch S_(a,1)    is now turned off with zero current I_(aux). Current flows into    V_(out)+ from V_(in) ⁺ through inductor 500 b, and through main    switch S_(m,3) Current now flows into V_(in) ⁻ from V_(out) ⁻ to    through main switch S_(m,2) and through inductor 500 a.

Similar switching steps occur when the current at the main inductor 500is reverse in polarity. Switch pairs (S_(m,1), S_(m,2)), (S_(m,4),S_(m,3)), (S_(a,1), S_(a,2)) and diodes (D₂, D₁) are swapped at theabove description to accomplish this symmetrical case.

The definite articles “a”, “an” is used herein, such as “a converter”,“a switch” have the meaning of “one or more” that is “one or moreconverters” or “one or more switches”.

Although selected embodiments of the present invention have been shownand described, it is to be understood the present invention is notlimited to the described embodiments. Instead, it is to be appreciatedthat changes may be made to these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined bythe claims and the equivalents thereof.

1. A method for providing non-resonant zero-current switching in aswitching power converter operating in a continuous current mode, saidswitching power converter converting power from input power to outputpower, said switching power converter including a main switch connectedto at least one main inductor, wherein an auxiliary inductor isconnectible with the main inductor, wherein main current flows from aninput to an output, the method comprising the steps of: directlyconnecting, in parallel, the auxiliary inductor with the main inductorthereby charging the auxiliary inductor so that an auxiliary currentflows from the output to the input opposing said main current, thedirect connecting avoiding the input, the output, and ground; and upon atotal current substantially equaling zero, switching on the main switch,wherein said total current includes a sum of said main current and saidauxiliary current.
 2. The method according to claim 1, furthercomprising the step of: disconnecting the auxiliary inductor from themain inductor when said auxiliary current is substantially orapproaching zero current.
 3. A switching converter including at leastone stage selected from the group consisting of a buck stage and a booststage, said at least one stage comprising: a main switch connecting aninput voltage terminal to a first node; a main inductor connected at oneend to said first node and at the other end operatively connected at asecond node to a voltage output; and an auxiliary inductor adapted forconnecting directly in parallel with the main inductor between saidfirst and second nodes, wherein the auxiliary inductor does not connectto the main inductor through any of the input voltage, the voltageoutput, or ground.
 4. The switching converter of claim 3: wherein, uponsaid connecting the auxiliary inductor with the main inductor, chargingsaid auxiliary inductor so that an auxiliary current flows from thesecond node to the first node opposing main current flowing between saidfirst and second nodes through said main inductor, wherein a totalcurrent includes a sum of said main current and said auxiliary current,and wherein, upon a total current substantially equaling zero, said mainswitch is switched on, and energy stored within the auxiliary inductoris substantially all available for converting to output power by theswitching converter.
 5. The switching converter according to claim 3,further comprising: a first auxiliary switch adapted for connecting saidauxiliary inductor to said first node; and a second auxiliary switchadapted for connecting said auxiliary inductor to said second node. 6.The switching converter according to claim 3, further comprising: adischarge diode connecting said auxiliary inductor to a second inputvoltage terminal or ground.
 7. The switching converter according toclaim 5, wherein said first and second auxiliary switches areimplemented as field-effect transistors each with parallel connectedparasitic diodes, wherein the parasitic diodes are connected in oppositedirections.
 8. The switching converter according to claim 3, whereinsaid main switch is selected from the group consisting of: a siliconcontrolled rectifier (SCR), an insulated gate bipolar junctiontransistor (IGBT), a bipolar junction transistor (BJT), a field effecttransistor (FET), a junction field effect transistor (JFET), a switchingdiode, an electrical relay, a reed relay, a solid state relay, aninsulated gate field effect transistor (IGFET), a diode for alternatingcurrent (DIAC), and/or a triode for alternating current TRIAC.
 9. Aswitching converter comprising: a plurality of main switchesinterconnected in a full bridge topology, said main switches including afirst switch, a second switch, a third switch and a fourth switch,wherein a pair of input voltage terminals are attachable at a first nodeconnecting said first and third switches and at a second node connectingsaid second and fourth switches; wherein a first output voltage terminalis operatively attached at a third node connecting said third and fourthswitches and a second output voltage terminal is operatively attached ata fourth node connecting said first and second switches; a first maininductor attachable between said first output voltage terminal and saidthird node; a second main inductor attachable between said second outputvoltage terminal and said fourth node; and an auxiliary inductorconnectible between said third node and said fourth node.
 10. Theswitching converter according to claim 9, wherein, upon connecting theauxiliary inductor with said at least one of said first and second maininductors thereby charging the auxiliary inductor so that an auxiliarycurrent flows between said third node and said fourth node, saidauxiliary current opposes said main current, wherein a total currentincludes a sum of said main current and said auxiliary current, andwherein said main switches are switched on when said total currentsubstantially equals or approaches zero current, and energy storedwithin said auxiliary inductor is substantially all available forconverting to output power by the switching converter.
 11. The switchingconverter according to claim 9, further comprising: a first auxiliaryswitch adapted for connecting said auxiliary inductor to said thirdnode; and a second auxiliary switch adapted for connecting saidauxiliary inductor to said fourth node.
 12. The switching converteraccording to claim 11, wherein said first and second auxiliary switchesare implemented as field-effect transistors each with parasitic diodes,wherein said parasitic diodes are connected on opposite directions. 13.The switching converter according to claim 9, further comprising: atleast one discharge diode connecting said auxiliary conductor to saidsecond node.
 14. The switching converter according to claim 9, whereinsaid first inductor and said second inductor are split inductors. 15.The switching converter according to claim 9, wherein main switches areselected from the group consisting of: a silicon controlled rectifier(SCR), an insulated gate bipolar junction transistor (IGBT), a bipolarjunction transistor (BJT), a field effect transistor (FET), a junctionfield effect transistor (JFET), a switching diode, an electrical relay,a reed relay, a solid state relay, an insulated gate field effecttransistor (IGFET), a diode for alternating current (DIAC), and a triodefor alternating current TRIAC.
 16. The method according to claim 1,wherein the main inductor and the auxiliary inductor are not adapted formagnetic coupling.
 17. The switching converter of claim 3, wherein themain inductor and the auxiliary inductor are not adapted for magneticcoupling.